1. Field of Invention
The present invention relates to an electrical connection box, particularly an electrical connection box that is mounted in an engine room or other space of a vehicle, such as an automobile. Especially, the present invention relates to an electrical connection box capable of accommodating electrical circuits at high density, which circuits are to be connected to a large number of external circuits, such as relays and fuses, enabling efficient branch connection of wire harnesses. More particularly, the present invention relates to an electrical connection box accommodating internal circuits composed of electric wires and terminals connected therewith by pressure grip connections and internal circuits composed of bus bars.
2. Description of Related Art
In a conventional vehicle electrical connection box of this kind having internal circuits composed of electrical wires and terminals connected therewith by pressure gripping and internal circuits composed of bus bars formed by punching electrically conductive metal plates, a power source input circuit for receiving electric power from an alternator is composed of the bus bars, and other circuits are composed of single-core electric wires and the terminals connected therewith.
Functional parts such as relays, fuses, connectors, and the like are mounted on upper and lower surfaces of a casing of the box. Tabs (terminals for connecting internal circuits and external circuits with each other) project from the upper and lower surfaces of the casing to enable connection of the tabs with the functional parts.
JP-A-9-23539, published Jan. 21, 1997, shows one electrical connection box of this type. Inside the casing are a stack of bus bars and insulating layers, and a plate that lies on the stack. The plate has, on its side away from the stack, upstanding walls that provide grooves in which electrical wires lie. Terminal members make pressure grip connections with the wires in the grooves and have tab portions that project through the plate to make connection with the bus bars. Tabs of the bus bars project through the casing to make connection with exterior circuits, e.g. fuse boxes and relay boxes.
While this prior art construction enables an easy solution of the arrangement of the electrical wires and the terminal members connected to them, there are conflicting requirements for the efficient construction and operation of such connection boxes that are not fully meet.
The accommodation of many electrical wires in the box increases the volume, particularly the thickness of the box. Using electric wires and the terminals is advantageous because circuit alterations can be accomplished easily at a low cost, but disadvantageous because each such circuit has two electrical contact portions in its connection path, one of which is formed between a terminal and a wire and the other of which is formed between the terminal and another element. It is preferable to form a circuit of a bus bar because in this case the circuit is allowed to have only one contact portion in its connection path between an external terminal and a tab projecting from the bus bar. A circuit having only one contact portion is in general preferable to a circuit having two contact portions in respect of the reliability to its electrical contact performance.
However, a stack of bus bars and insulation layers interposed between them also increases the thickness of the electrical connection box.
The number of internal wire circuits of the electrical connection box has tended to increase because the number of electric components on or in a vehicle body has been increasing. The increase of the number of circuits has lead to the use of a large electrical connection box. Consequently, it has become difficult to find space for the electrical connection box when mounting it in the engine room or the like of the vehicle body.